Dispersion compensation for a frequency-modulated continuous-wave (FMCW) LIDAR system

ABSTRACT

An oscillator system includes a transmitter configured to transmit a frequency modulated continuous wave (FMCW) light beam along a transmission path, where the FMCW light beam includes a plurality of wavelength ramps and a wavelength of the FMCW light beam continuously varies over time; an oscillator structure configured to oscillate about a scanning axis based on a deflection angle of the oscillator structure that continuously varies over time; and a dispersive element arranged in the transmission path and configured to receive the FMCW light beam and output a compensated FMCW light beam along the transmission path, where the dispersive element is configured to compensate for a propagation direction disturbance caused by an oscillation of the oscillator structure. The oscillator structure is arranged in the transmission path and is configured to direct the FMCW light beam or the compensated FMCW light beam towards an output of the transmission path.

FIELD

The present disclosure relates generally to a frequency-modulatedcontinuous-wave (FMCW) Light Detection and Ranging (LIDAR) system.

BACKGROUND

Light Detection and Ranging (LIDAR), is a remote sensing method thatuses light, such as transmitted laser beams, to measure ranges (variabledistances) to one or more objects in a field of view. In particular, amicroelectromechanical system (MEMS) mirror is used to scan light acrossthe field of view. Arrays of photodetectors receive reflections fromobjects illuminated by the light, and a time-of-flight (ToF) it takesfor the reflections to arrive at various sensors in the photodetectorarray is determined. LIDAR systems form depth measurements and makedistance measurements by mapping the distance to objects based on thetime-of-flight computations. Thus, the time-of-flight computations cancreate distance and depth maps, which may be used to generate images.

Indirect ToF three-dimensional image (3DI) sensors are based oncontinuously modulated light for scene illumination, and demodulation ofthe received light on a pixel level during integration phases. Inparticular, continuous wave modulation uses continuous light beamsinstead of short light pulses and the modulation is done in terms offrequency of sinusoidal waves.

A scan such as an oscillating horizontal scan (e.g., from left to rightand right to left of a field of view) can illuminate a scene in acontinuous scan fashion. Since the light is transmitted continuously,the light transmitted by one or more light sources results in a scanline that continuously moves across the field of view as the (MEMS)mirror rotates about an axis. Thus, an area referred to as the field ofview can be scanned and objects within the area can be detected andimaged.

For continuous wave modulation, such as that used for afrequency-modulated continuous-wave (FMCW) beam, a detected wave afterreflection has a shifted frequency and/or phase, and the shift isproportional to distance from reflecting object or surface. Thus, thedistance can be determined from the measured shift. This is in contrastto pulsed modulation, in which a system measures distance to a 3D objectby measuring the absolute time a light pulse takes to travel from asource into the 3D scene and back, after reflection.

However, an issue arises when implementing continuous scanning of a FMCWbeam due to the changing wavelength (frequency) of the beam incombination with the continuous scanning motion of the MEMS mirror. Dueto the mirror motion and the wavelength sweep of the FMCW beam, thepropagation direction of the light beam is wavelength (frequency)dependent. As a result, all wavelengths of the FMCW beam cannot bedirected at the same point on a target which disrupts the FMCWmeasurement principle.

Therefore, an improved FMCW LIDAR system that can compensate for thisdispersion effect may be desirable.

SUMMARY

One or more embodiments provide an oscillator system that includes atransmitter configured to transmit a frequency modulated continuous wave(FMCW) light beam along a transmission path, where the FMCW light beamincludes a plurality of wavelength ramps and a wavelength of the FMCWlight beam continuously varies over time; an oscillator structureconfigured to oscillate about a scanning axis based on a deflectionangle of the oscillator structure that continuously varies over time;and a dispersive element arranged in the transmission path andconfigured to receive the FMCW light beam and output a compensated FMCWlight beam along the transmission path, wherein the dispersive elementis configured to compensate for a propagation direction disturbancecaused by an oscillation of the oscillator structure. The oscillatorstructure is arranged in the transmission path and is configured todirect the FMCW light beam or the compensated FMCW light beam towards anoutput of the transmission path.

One or more embodiments provide an oscillator system that includes atransmitter configured to transmit a frequency modulated continuous wave(FMCW) light beam along a transmission path, where the FMCW light beamincludes a plurality of wavelength ramps and a wavelength of the FMCWlight beam continuously varies over time; and an oscillator structureconfigured to oscillate about a scanning axis based on a deflectionangle of the oscillator structure that continuously varies over time.The oscillator structure is arranged in the transmission path and isconfigured to receive the FMCW light beam at a reflective surface.Additionally, the reflective surface is a micro-structured surfaceconfigured to compensate for a propagation direction disturbance causedby an oscillation of the oscillator structure such that each wavelengthof a corresponding wavelength ramp of the FMCW light beam is reflectedby the reflective surface in a same direction along transmission path.

One or more embodiments provide a method of controlling an oscillatorstructure. The method includes transmitting a frequency modulatedcontinuous wave (FMCW) light beam along a transmission path, where theFMCW light beam includes a plurality of wavelength ramps and awavelength of the FMCW light beam continuously varies over time; drivingan oscillator structure about a scanning axis based on a deflectionangle of the oscillator structure that continuously varies over time,where the oscillator structure is arranged in the transmission path andis configured to direct the FMCW light beam or a compensated FMCW lightbeam that is derived from the FMCW light beam towards an output of thetransmission path; and synchronizing the wavelength of the FMCW lightbeam with the deflection angle of the oscillator structure.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments are described herein making reference to the appendeddrawings.

FIG. 1 illustrates a dependency of a wavelength (frequency) of a FMCWlight beam based on deflection angle θ of a microelectromechanicalsystem (MEMS) mirror according to one of more embodiments;

FIG. 2A illustrates a further dependency of a wavelength (frequency) ofa FMCW light beam based on deflection angle θ of amicroelectromechanical system (MEMS) mirror according to one of moreembodiments;

FIG. 2B illustrates a correlation of different wavelength ramps shownFIG. 2A to different dedicated transmission directions according to oneof more embodiments;

FIG. 3 shows a FMCW LIDAR system according to one or more embodiments;

FIG. 4 shows another FMCW LIDAR system according to one or moreembodiments; and

FIG. 5 shows another FMCW LIDAR system according to one or moreembodiments.

DETAILED DESCRIPTION

In the following, various embodiments will be described in detailreferring to the attached drawings. It should be noted that theseembodiments serve illustrative purposes only and are not to be construedas limiting. For example, while embodiments may be described ascomprising a plurality of features or elements, this is not to beconstrued as indicating that all these features or elements are neededfor implementing embodiments. Instead, in other embodiments, some of thefeatures or elements may be omitted, or may be replaced by alternativefeatures or elements. Additionally, further features or elements inaddition to the ones explicitly shown and described may be provided, forexample conventional components of sensor devices.

Features from different embodiments may be combined to form furtherembodiments, unless specifically noted otherwise. Variations ormodifications described with respect to one of the embodiments may alsobe applicable to other embodiments. In some instances, well-knownstructures and devices are shown in block diagram form rather than indetail in order to avoid obscuring the embodiments.

Connections or couplings between elements shown in the drawings ordescribed herein may be wire-based connections or wireless connectionsunless noted otherwise. Furthermore, such connections or couplings maybe direct connections or couplings without additional interveningelements or indirect connections or couplings with one or moreadditional intervening elements, as long as the general purpose of theconnection or coupling, for example to transmit a certain kind of signalor to transmit a certain kind of information, is essentially maintained.

Embodiments relate to optical sensors and optical sensor systems and toobtaining information about optical sensors and optical sensor systems.A sensor may refer to a component which converts a physical quantity tobe measured to an electric signal, for example a current signal or avoltage signal. The physical quantity may, for example, compriseelectromagnetic radiation, such as visible light, infrared (IR)radiation, or other type of illumination signal, a current, or avoltage, but is not limited thereto. For example, an image sensor may bea silicon chip inside a camera that converts photons of light comingfrom a lens into voltages. The larger the active area of the sensor, themore light that can be collected to create an image.

A sensor device as used herein may refer to a device which comprises asensor and further components, for example biasing circuitry, ananalog-to-digital converter or a filter. A sensor device may beintegrated on a single chip, although in other embodiments a pluralityof chips or also components external to a chip may be used forimplementing a sensor device.

In frequency-modulated continuous-wave (FMCW) Light Detection andRanging (LIDAR) systems, a light source continuously transmits a FWCMlight beam into a field of view and the light reflects from one or moreobjects by backscattering. In particular, FWCM LIDAR is an indirectTime-of-Flight (TOF) system during which the frequency or wavelength ofa transmitted light beam is continuously swept between a minimum valueand a maximum value that define a predefined frequency/wavelength rangeor band. For example, the frequency or wavelength of the transmittedlight beam may be modulated according to a triangle-wave modulationpattern comprised of a series of frequency or wavelength ramps.

FIG. 1 illustrates a dependency of a wavelength (frequency) of a FMCWlight beam based on deflection angle θ of a microelectromechanicalsystem (MEMS) mirror according to one of more embodiments. A deflectionangle θ may be a tilt angle, a rotation angle, a mirror position, arotation position, or any other reference to a position of the MEMSmirror with respect to its scanning axis. Hence, these position termsmay be used interchangeably herein.

FIG. 1 includes a top diagram and bottom diagram. The top diagram ofFIG. 1 shows a wavelength ramp of a FMCW light beam used for FMCWranging in one or more embodiments. The wavelength ramp includes aforward ramp (up-ramp) portion and a backward ramp (down-ramp) portion.Thus, different wavelengths are transmitted at different times.

The bottom diagram of FIG. 1 shows a deflection angle θ of a MEMS mirrorover time as the MEMS mirror performs a scanning operation, with amovement of the MEMS mirror being from right-to-left (i.e.,counterclockwise) during the forward ramp of the wavelength ramp andbeing from left-to-right (i.e., clockwise) during the backward ramp ofthe wavelength ramp. Both the wavelength of the FMCW light beam and thedeflection angle θ of the MEMS mirror are constantly changing over time.Thus, different wavelengths of the FMCW light beam are incident on theMEMS mirror at different transmission times and at different deflectionangle θ.

As a result, different wavelengths of the FMCW light beam are dispersedand directed in different directions by the MEMS mirror despite theintention to transmit all wavelengths of at a same direction.Consequently, all wavelengths of the FMCW light beam cannot be directedat the same point on a target, which disrupts the FMCW measurementprinciple.

A length L of the wavelength/frequency ramp is equivalent to an amountof time (i.e., a duration) it takes for the wavelength to change from aminimum wavelength to a maximum wavelength or vice versa. The length Lof the forward ramp (up-ramp) portion and the backward ramp portion maybe equal. Thus, one triangle wave interval is 2 L in duration. It isalso to be noted that the length L, and consequently a length of atriangle wave interval, of the wavelength/frequency ramp is adjustableby a controller of the FMCW LIDAR system. For example, the controllercan adjust the slope and thus the length L of the ramp according to theoscillation frequency of the MEMS mirror. In this way, the length L ofthe ramp can be synchronized with the MEMS mirror motion, particularlywith the angular range of motion from a zero tilt angle to a maximumtilt angle. For example, each wavelength of the FMCW light beam ismapped to a specific deflection angle and the continuous change of thewavelength is synchronized with a continuous change of the deflectionangle. Thus, the wavelength changes in step with the deflection angle ofthe MEMS mirror.

In this case a minimum wavelength of the wavelength ramp is mapped to azero tilt angle and a maximum wavelength of the wavelength ramp ismapped to a maximum tilt angle. Alternatively, this could be reversedwhere a minimum wavelength of the wavelength ramp is mapped to a maximumtilt angle and a maximum wavelength of the wavelength ramp is mapped toa zero tilt angle. A sensing circuit may be further provided to sense arotational or deflection position (e.g., the rotation angle θ of theMEMS mirror) in order to provide further feedback information to thecontroller in order to aid in the synchronization.

FIG. 2A illustrates a further dependency of a wavelength (frequency) ofa FMCW light beam based on deflection angle θ of amicroelectromechanical system (MEMS) mirror according to one of moreembodiments. FIG. 2A includes a top diagram and bottom diagram.

The top diagram of FIG. 2A shows a series or plurality of wavelengthramps of a FMCW light beam used for FMCW ranging in one or moreembodiments. The wavelength ramps include a series of N forward ramps(up-ramps) and a series of N backward ramps (down-ramps), wherein N isan integer greater than zero and a total number of wavelength ramps overa full period of a MEMS mirror motion is 2N. Thus, different wavelengthsare transmitted at different times.

The bottom diagram of FIG. 2A shows a deflection angle θ of a MEMSmirror over time as the MEMS mirror performs a scanning operation, witha movement of the MEMS mirror being from right-to-left (i.e.,counterclockwise) during the forward ramp of the wavelength ramp andbeing from left-to-right (i.e., clockwise) during the backward ramp ofthe wavelength ramp. Both the wavelength of the FMCW light beam and thedeflection angle θ of the MEMS mirror are constantly changing over time.Thus, different wavelengths of the FMCW light beam are incident on theMEMS mirror at different transmission times and at different deflectionangle θ.

In particular, multiple ramps can fit into a half period HP of the MEMSmirror motion. In this case, a series of consecutive N forward ramps aregenerated during a first half period of one period of the MEMS mirrormotion, and a series of consecutive N backward ramps are generatedduring a second half period of the same period of the MEMS mirrormotion. The two series of consecutive N ramps may also be reversed suchthat the series of consecutive N backward ramps are generated during thefirst half period and the series of consecutive N forward ramps aregenerated during the second half period. Nevertheless, in one period,the series of consecutive N forward ramps and the series of consecutiveN backward ramps are contiguous in that the last ramp in the firstseries and the first ramp in the second series join at a maximumdeflection angle of the MEMS mirror to form a triangle.

It is at the maximum deflection angle that the MEMS mirror alters isdirection of motion. Thus, in order to make dispersion compensationalways functional it is necessary to alter the direction of thewavelength ramps at the moment when the MEMS mirror is altering itsdirection of motion (i.e., maximum deflection angle). In other words, alight beam transmitter changes the direction of the ramps from forwardsto backwards or from backwards to forwards at the maximum deflectionangle of the MEMS mirror. The pattern of forward and backward wavelengthramps then repeats for the next MEMS mirror motion period.

Additionally, each wavelength ramp has a length L that is equivalent toan amount of time (i.e., a duration) it takes for the wavelength tochange from a minimum wavelength to a maximum wavelength or vice versa.Here, a mirror period can be defined as 2N*L.

The length L of the wavelength ramps is adjustable by a controller ofthe FMCW LIDAR system. For example, the controller can adjust the slopeand thus the length L of the ramps according to the oscillationfrequency of the MEMS mirror. In this way, the length L of the ramps canbe synchronized with the MEMS mirror motion. Particularly, thecontroller can assign (i.e., map) and synchronize each ramp with asub-range or segment of the full angular range of the MEMS mirror, as isshown in FIG. 2A. For example, the first wavelength ramp is synchronizedto a first angular sub-range of the MEMS mirror motion, the secondwavelength ramp is synchronized to a second angular sub-range of theMEMS mirror motion, and the final wavelength ramp 2N is synchronized toa last angular sub-range of the MEMS mirror motion. In each angularsub-range, the transmitter varies (i.e., ramps) the wavelength insynchronization with change in the deflection angle of the MEMS mirror.As a result, the continuous change of the wavelength is synchronizedwith a continuous change of the deflection angle. Thus, the wavelengthchanges in step with the deflection angle of the MEMS mirror.

Additionally, FIG. 2B illustrates a correlation of different wavelengthramps shown FIG. 2A to different dedicated transmission directionsaccording to one of more embodiments. In particular, FIG. 2B shows atransmission direction of a subset of wavelength ramps (i.e., wavelengthramps 1, 2, and 3) of a FMCW light beam, where each directional beam 1,2, and 3 corresponds to a different wavelength ramp 1, 2, and 3 of theFMCW light beam shown in the top diagram of FIG. 2A. Each wavelengthramp 1 to 2N addresses a dedicated beam propagation angle (i.e., adedicated transmission direction). Each dedicated beam propagation anglewill be addressed twice: once during ramp up (e.g., during acounterclockwise MEMS mirror motion) and again during ramp down (e.g.,during a clockwise MEMS mirror motion). Thus, symmetrically opposed ramppairs that are equidistant from the half-period mark (i.e., from themaximum deflection angle), such as first and final ramps, are assignedto the same angular sub-range but to different MEMS mirror motiondirections.

All wavelengths in each wavelength ramp will propagate to the samedirection due to dispersion compensation that is realized in theembodiments described herein. In order to address N angular positions(i.e., N dedicated transmission directions), it is necessary to have Nup and N down ramps for a total 2N wavelength ramps.

FIG. 3 shows a FMCW LIDAR system 300 according to one or moreembodiments. The FMCW LIDAR system 300 includes a transmitter 10 thatincludes a plurality of light sources 11 (e.g., laser diodes or lightemitting diodes) that are configured to transmit a FMCW light beam alonga transmission path 13 or channel. The light sources 11 may be linearlyaligned in a single bar formation and are configured to transmit lightused for scanning a field of view. The light emitted by the lightsources is typically infrared light although light with anotherwavelength might also be used. The transmitter 10 may generate the FMCWlight beam according to the wavelength ramping pattern shown in eitherFIG. 1 or FIG. 2A. As will be described below, the wavelength ramps maybe synchronized with a corresponding angular range of a MEMS mirrormotion with the aid of a controller 23 in accordance with thesynchronization schemes described in conjunction with FIGS. 1, 2A, and2B

The shape of the light emitted by the light sources may be spread in adirection perpendicular to the transmission direction to form a lightbeam with an oblong shape perpendicular to a transmission direction. Theillumination light transmitted from the light sources 11 is directedtowards an oscillating MEMS mirror 15 and a transmitter optics 18 (i.e.,a dispersive element). Thus, the FMCW LIDAR system 300 further includesa MEMS mirror 15 and a dispersive element 18 that are arranged along thetransmission path 13. In this embodiment, the dispersive element 18 isarranged “downstream” from the MEMS mirror 15 along the transmissionpath 13. However, as shown in FIG. 4, the dispersive element 18 may bearranged “upstream” from the MEMS mirror 15 along the transmission path13.

The MEMS mirror 15 is a mechanical moving mirror (i.e., a MEMSmicro-mirror) integrated on a semiconductor chip (not shown). It isconfigured to oscillate about a scanning axis 16 such that its angle ofrotation θ changes to perform a scanning operation. The MEMS mirror 15itself is a resonator (i.e., a resonant MEMS mirror) configured tooscillate “side-to-side” about the scanning axis 16 at a resonancefrequency such that the light reflected from the MEMS mirror 15oscillates back and forth in a scanning direction. The reflected lightmay form a vertical scanning line of light that oscillates back andforth in a horizontal scanning direction or it may form a horizontalscanning line of light that oscillates back and forth in a verticalscanning direction. A scanning period or an oscillation period isdefined, for example, by one complete oscillation from a first edge ofthe field of view (e.g., left side) to a second edge of the field ofview (e.g., right side) and then back again to the first edge. A mirrorperiod of the MEMS mirror 15 corresponds to a scanning period.

Thus, the field of view is scanned in the scanning direction by a bar oflight by changing the deflection angle θ of the MEMS mirror 15 on itsscanning axis 16. For example, the MEMS mirror 15 may be configured tooscillate at a resonance frequency of 2 kHz, between +/−15 degrees tosteer the light over +/−30 degrees making up the scanning range of thefield of view. Thus, the field of view may be scanned, line-by-line, bya rotation of the MEMS mirror 15 through its degree of motion. One suchsequence through the degree of motion (e.g., from −15 degrees to +15degrees) is referred to as a single scan or scanning cycle. Multiplescans may be used to generate distance and depth maps, as well as 3Dimages by a processing unit.

While the transmission mirror is described in the context of a MEMSmirror, it will be appreciated that other mirrors can also be used. Inaddition, the resonance frequency or the degree of rotation is notlimited to 2 kHz and +/−15 degrees, respectively, and both the resonancefrequency and the field of view may be increased or decreased accordingto the application.

The dispersive element 18 may be a prism, a diffractive grating, orother dispersive structure that is capable of compensating thepropagation direction disturbance caused by the MEMS mirror 15 viadispersion. As a result of the dispersive element 18 being arranged inthe transmission path 13 downstream from the MEMS mirror 15, the FMCWlight beam that is directed (by reflection) by the MEMS mirror 15 iscompensated such that all wavelengths of a particular wavelength ramp ofthe FMCW light beam are directed at a same point on a target, therebyenabling FMCW ToF measurements. In this example, three wavelengths A, B,and C of a particular wavelength ramp (e.g., selected from wavelengthramps 1 to 2N) that are diverging from a point on a target due theoscillation of the MEMS mirror 15 are shown being aligned by thedispersive element 18 with the point on the target (i.e., being alignedwith a same transmission direction). Thus, each wavelength of aparticular wavelength ramp of the FMCW light beam is aligned in a samedirection at an output of the transmission path 13.

The FMCW LIDAR system 300 further includes a system controller 23 and aMEMS driver 25. The system controller 23 is configured to controlcomponents of the FMCW LIDAR system 300. Thus, the system controller 23includes control circuitry, such as a microcontroller, that isconfigured to generate control signals. In this example, the controlsignals may be used to control a function of the transmitter 10 (i.e., afunction of the light sources 11) and the MEMS driver 25. For example,the system controller 23 may control the oscillation frequency and theoscillation range (angular range of motion) of the MEMS mirror 15.Additionally, the system controller 23 may control the length L of thewavelength ramps of the FMCW light beam in order to synchronize thelength L with the angular range or sub-range of motion of the MEMSmirror 15, as described above in conjunction with FIGS. 1, 2A, and 2B.As such, each wavelength of the FMCW light beam is mapped by the systemcontroller 23 to one or more specific deflection angles and thecontinuous change of the wavelength is synchronized with a continuouschange of the deflection angle.

The MEMS driver 25 is configured to drive the MEMS mirror 15. Inparticular, the MEMS driver 25 actuates and senses the rotation positionof the mirror, and provides position information (e.g., tilt angle ordegree of rotation about the rotation axis) of the mirror to the systemcontroller 23. Thus, the MEMS driver 25 includes a measurement circuitconfigured to measure the rotation position of the mirror.

For example, an actuator structure that is used to drive the MEMS mirror15 may be a comb-drive rotor and stator that include two drivecapacitors whose capacitance or stored charge is deflection angledependent. Thus, the measurement circuit may determine the rotationposition by measuring the capacitances of the drive capacitors or theirstored charges.

Based on this position information, the system controller 23 may adjustthe length L of the wavelength ramp to ensure synchronization betweenthe wavelength of the FMCW light beam and the deflection angle of theMEMS mirror 15 is maintained.

FIG. 4 shows a FMCW LIDAR system 400 according to one or moreembodiments. The FMCW LIDAR system 400 is similar to FMCW LIDAR system300 with the exception that the dispersive element 18 is arrangedupstream from the MEMS mirror 15 along the transmission path 13. In thiscase, the dispersive element 18 introduces a pre-distortion to the FMCWlight beam in anticipation of the propagation direction disturbancecaused by the oscillation of the MEMS mirror 15. In other words, thedispersive element 18 provides pre-compensation such that differentwavelengths of the FMCW light beam are dispersed or spread by thedispersive element 18 in different directions along the transmissionpath 13 towards the MEMS mirror 15. This may also be referred to as abeam compensative tilt. Upon being incident on the MEMS mirror 15, eachwavelength of a particular wavelength ramp is aligned with the samepoint on a target despite each wavelength of the wavelength ramp beingdeflected at a different deflection angle θ of the MEMS mirror 15. Thus,each wavelength of a particular wavelength ramp of the FMCW light beamis transmitted in the same transmission direction/angle by the system400.

The FMCW LIDAR system 400 further includes a system controller 23 and aMEMS driver 25 as similarly described above for performingsynchronization between the wavelength of the FMCW light beam and thedeflection angle of the MEMS mirror 15.

FIG. 5 shows a FMCW LIDAR system 500 according to one or moreembodiments. In this example, the MEMS mirror 15 has a micro-structuredMEMS surface 17, such as a diffractive grating. As a result, the FMCWlight beam propagation compensation is introduced at the reflectivesurface of the MEMS mirror as the FMCW light beam is reflected by themicro-structured MEMS surface 17. Thus, each wavelength of a particularwavelength ramp of the FMCW light beam is transmitted in the sametransmission direction/angle by the system 500.

The FMCW LIDAR system 500 further includes a system controller 23 and aMEMS driver 25 as similarly described above for performingsynchronization between the wavelength of the FMCW light beam and thedeflection angle of the MEMS mirror 15.

Additional embodiments are provided below:

Embodiment 1 includes an oscillator system, comprising: a transmitterconfigured to transmit a frequency modulated continuous wave (FMCW)light beam along a transmission path, wherein the FMCW light beamcomprises a plurality of wavelength ramps and a wavelength of the FMCWlight beam continuously varies over time; and an oscillator structureconfigured to oscillate about a scanning axis based on a deflectionangle of the oscillator structure that continuously varies over time,wherein the oscillator structure is arranged in the transmission pathand is configured to receive the FMCW light beam at a reflectivesurface, and wherein the reflective surface is a micro-structuredsurface configured to compensate for a propagation direction disturbancecaused by an oscillation of the oscillator structure such that eachwavelength of a corresponding wavelength ramp of the FMCW light beam isreflected by the reflective surface in a same direction alongtransmission path.

Embodiment 2 includes the oscillator system of embodiment 1, wherein themicro-structured surface is a diffractive grating.

Embodiment 3 includes the oscillator system of embodiment 1, furthercomprising: a controller configured to synchronize the wavelength of theFMCW light beam with the deflection angle of the oscillator structure.

Embodiment 4 includes the oscillator system of embodiment 3, wherein thecontroller is configured to synchronize the wavelength of the FMCW lightbeam with the deflection angle of the oscillator structure such that thewavelength of the FMCW light beam varies in synchronization with avariance in the deflection angle of the oscillator structure.

Embodiment 5 includes the oscillator system of embodiment 3, wherein thecontroller is configured to synchronize the wavelength of the FMCW lightbeam with the deflection angle of the oscillator structure such thateach wavelength of the FMCW light beam is mapped to a differentdeflection angle of a plurality of deflection angles as the deflectionangle varies over time.

Embodiment 6 includes the oscillator system of embodiment 3, wherein thecontroller is configured to synchronize the wavelength of the FMCW lightbeam with the deflection angle of the oscillator structure such that thelength of the forward ramps and the backward ramps is synchronized withan angular range of the deflection angle of the oscillator structure.

Embodiment 7 includes the oscillator system of embodiment 6, wherein thecontroller is configured to control the length of the forward ramps andthe backward ramps in order to synchronize the length with the angularrange of the deflection angle of the oscillator structure.

Embodiment 8 includes the oscillator system of embodiment 6, wherein:the minimum wavelength of the FMCW light beam is synchronized with azero deflection angle of the oscillator structure and the maximumwavelength of the FMCW light beam is synchronized with a maximumdeflection angle of the oscillator structure, or the minimum wavelengthof the FMCW light beam is synchronized with the maximum deflection angleof the oscillator structure and the maximum wavelength of the FMCW lightbeam is synchronized with the zero deflection angle of the oscillatorstructure.

Embodiment 9 includes the oscillator system of embodiment 1, wherein thecontroller is configured to synchronize a continuous variance of thewavelength of the FMCW light beam with a continuous variance of thedeflection angle of the oscillator structure.

Embodiment 10 includes the oscillator system of embodiment 1, furthercomprising: a measurement circuit configured to measure the deflectionangle of the oscillator structure as the deflection angle varies overtime and generate position information based on the measured deflectionangle, wherein the controller is configured to synchronize thewavelength of the FMCW light beam with the deflection angle of theoscillator structure based on the position information.

Embodiment 11 includes the oscillator system of embodiment 1, whereinthe plurality of wavelength ramps correspond to an oscillation period ofthe oscillator structure, the plurality of wavelength ramps including aseries of consecutive forward ramps generated over a first half-periodof the oscillation period and a series of consecutive backward rampsgenerated over a second half-period of the oscillation period.

Embodiment 12 includes the oscillator system of embodiment 11, whereinthe series of consecutive forward ramps includes N forward ramps and theseries of consecutive backward ramps includes N backward ramps, whereinN is an integer greater than zero.

Embodiment 13 includes the oscillator system of embodiment 11, whereinthe transmitter is configured to change a ramping direction of theplurality of wavelength ramps at a maximum deflection angle of theoscillator structure.

Embodiment 14 includes the oscillator system of embodiment 11, whereineach wavelength ramp of the plurality of wavelength ramps corresponds toone angular sub-range of a plurality of angular sub-ranges that make upa full angular range of the deflection angle of the oscillatorstructure.

Embodiment 15 includes the oscillator system of embodiment 14, wherein:each wavelength ramp of the series of consecutive forward rampscorresponds to a different angular sub-range of the full angular rangeof the deflection angle, and each wavelength ramp of the series ofconsecutive backward ramps corresponds to a different angular sub-rangeof the full angular range of the deflection angle.

Embodiment 16 includes the oscillator system of embodiment 14, wherein:each of the plurality of wavelength ramps have a length corresponding toa time duration each of the plurality of ramps takes to transitionbetween a minimum wavelength and a maximum wavelength, and theoscillator system further comprises: a controller configured to controlthe length of each of the plurality of wavelength ramps in order tosynchronize the length with an angular sub-range of the full angularrange of the deflection angle.

Embodiment 17 includes the oscillator system of embodiment 14, furthercomprising: a controller configured to synchronize each of the pluralityof wavelength ramps to a corresponding angular sub-range of theplurality of angular sub-ranges.

Embodiment 18 includes the oscillator system of embodiment 17, whereinthe controller is configured to synchronize the wavelength of the FMCWlight beam with the deflection angle of the oscillator structure suchthat the wavelength of each wavelength ramp varies in synchronizationwith a variance in the deflection angle over the corresponding angularsub-range.

Embodiment 19 includes the oscillator system of embodiment 11, whereineach wavelength ramp of the plurality of wavelength ramps corresponds toone dedicated beam propagation direction of a plurality of dedicatedbeam propagation directions, and the micro-structured surface isconfigured to compensate the FMCW light beam such that each wavelengthof a same wavelength ramp is aligned in a same dedicated beampropagation direction at the output of the transmission path.

Embodiment 20 includes the oscillator system of embodiment 19, wherein:each wavelength ramp of the series of consecutive forward rampscorresponds to a different dedicated beam propagation direction of theplurality of dedicated beam propagation directions, and each wavelengthramp of the series of consecutive backward ramps corresponds to adifferent dedicated beam propagation direction of the plurality ofdedicated beam propagation directions.

Although embodiments described herein relate to a MEMS device with amirror, it is to be understood that other implementations may includeoptical devices other than MEMS mirror devices, including those notrelated to LIDAR. In addition, although some aspects have been describedin the context of an apparatus, it is clear that these aspects alsorepresent a description of the corresponding method, where a block ordevice corresponds to a method step or a feature of a method step.Analogously, aspects described in the context of a method step alsorepresent a description of a corresponding block or item or feature of acorresponding apparatus. Some or all of the method steps may be executedby (or using) a hardware apparatus, like for example, a microprocessor,a programmable computer or an electronic circuit. In some embodiments,some one or more of the method steps may be executed by such anapparatus.

While various embodiments have been described, it will be apparent tothose of ordinary skill in the art that many more embodiments andimplementations are possible within the scope of the disclosure.Accordingly, the invention is not to be restricted except in light ofthe attached claims and their equivalents. With regard to the variousfunctions performed by the components or structures described above(assemblies, devices, circuits, systems, etc.), the terms (including areference to a “means”) used to describe such components are intended tocorrespond, unless otherwise indicated, to any component or structurethat performs the specified function of the described component (i.e.,that is functionally equivalent), even if not structurally equivalent tothe disclosed structure that performs the function in the exemplaryimplementations of the invention illustrated herein.

Furthermore, the following claims are hereby incorporated into thedetailed description, where each claim may stand on its own as aseparate example embodiment. While each claim may stand on its own as aseparate example embodiment, it is to be noted that—although a dependentclaim may refer in the claims to a specific combination with one or moreother claims—other example embodiments may also include a combination ofthe dependent claim with the subject matter of each other dependent orindependent claim. Such combinations are proposed herein unless it isstated that a specific combination is not intended. Furthermore, it isintended to include also features of a claim to any other independentclaim even if this claim is not directly made dependent to theindependent claim.

It is further to be noted that methods disclosed in the specification orin the claims may be implemented by a device having means for performingeach of the respective acts of these methods.

Further, it is to be understood that the disclosure of multiple acts orfunctions disclosed in the specification or in the claims may not beconstrued as to be within the specific order. Therefore, the disclosureof multiple acts or functions will not limit these to a particular orderunless such acts or functions are not interchangeable for technicalreasons. Furthermore, in some embodiments a single act may include ormay be broken into multiple sub acts. Such sub acts may be included andpart of the disclosure of this single act unless explicitly excluded.

Instructions may be executed by one or more processors, such as one ormore central processing units (CPU), digital signal processors (DSPs),general purpose microprocessors, application specific integratedcircuits (ASICs), field programmable logic arrays (FPGAs), or otherequivalent integrated or discrete logic circuitry. Accordingly, the term“processor” or “processing circuitry” as used herein refers to any ofthe foregoing structure or any other structure suitable forimplementation of the techniques described herein. In addition, in someaspects, the functionality described herein may be provided withindedicated hardware and/or software modules. Also, the techniques couldbe fully implemented in one or more circuits or logic elements.

Thus, the techniques described in this disclosure may be implemented, atleast in part, in hardware, software, firmware, or any combinationthereof. For example, various aspects of the described techniques may beimplemented within one or more processors, including one or moremicroprocessors, DSPs, ASICs, or any other equivalent integrated ordiscrete logic circuitry, as well as any combinations of suchcomponents.

A controller including hardware may also perform one or more of thetechniques described in this disclosure. Such hardware, software, andfirmware may be implemented within the same device or within separatedevices to support the various techniques described in this disclosure.Software may be stored on a non-transitory computer-readable medium suchthat the non-transitory computer readable medium includes a program codeor a program algorithm stored thereon which, when executed, causes thecontroller, via a computer program, to perform the steps of a method.

Although various exemplary embodiments have been disclosed, it will beapparent to those skilled in the art that various changes andmodifications can be made which will achieve some of the advantages ofthe concepts disclosed herein without departing from the spirit andscope of the invention. It will be obvious to those reasonably skilledin the art that other components performing the same functions may besuitably substituted. It is to be understood that other embodiments maybe utilized and structural or logical changes may be made withoutdeparting from the scope of the present invention. It should bementioned that features explained with reference to a specific figuremay be combined with features of other figures, even in those notexplicitly mentioned. Such modifications to the general inventiveconcept are intended to be covered by the appended claims and theirlegal equivalents.

What is claimed is:
 1. An oscillator system, comprising: a transmitterconfigured to transmit a frequency modulated continuous wave (FMCW)light beam along a transmission path, wherein the FMCW light beamcomprises a plurality of wavelength ramps and a wavelength of the FMCWlight beam continuously varies over time; an oscillator structureconfigured to oscillate about a scanning axis based on a deflectionangle of the oscillator structure that continuously varies over time;and a dispersive element arranged in the transmission path andconfigured to receive the FMCW light beam and output a compensated FMCWlight beam along the transmission path, wherein the dispersive elementis configured to compensate for a propagation direction disturbancecaused by an oscillation of the oscillator structure, wherein theoscillator structure is arranged in the transmission path and isconfigured to direct the FMCW light beam or the compensated FMCW lightbeam towards an output of the transmission path.
 2. The oscillatorsystem of claim 1, wherein the dispersive element is arranged upstreamfrom the oscillator structure along the transmission path, and thedispersive element is configured to pre-compensate for the propagationdirection disturbance by dispersing each wavelength of the FMCW lightbeam in a different direction along the transmission path such that theoscillator structure aligns each wavelength of a correspondingwavelength ramp of the compensated FMCW light beam in a same direction.3. The oscillator system of claim 1, wherein the dispersive element isarranged downstream from the oscillator structure along the transmissionpath, and the dispersive element is configured to compensate for thepropagation direction disturbance by aligning each wavelength of acorresponding wavelength ramp of the FMCW light beam in a same directionto thereby output the compensated FMCW light beam.
 4. The oscillatorsystem of claim 1, wherein the dispersive element is configured tocompensate the FMCW light beam such that each wavelength of acorresponding wavelength ramp of the compensated FMCW light beam isaligned in a same direction at the output of the transmission path. 5.The oscillator system of claim 1, wherein the plurality of wavelengthramps including alternating forward ramps and backward ramps that form atriangle pattern.
 6. The oscillator system of claim 5, wherein theforward ramps and the backward ramps have a length corresponding to atime duration each of the plurality of ramps takes to transition betweena minimum wavelength and a maximum wavelength.
 7. The oscillator systemof claim 6, further comprising: a controller configured to synchronizethe wavelength of the FMCW light beam with the deflection angle of theoscillator structure.
 8. The oscillator system of claim 7, wherein thecontroller is configured to synchronize the wavelength of the FMCW lightbeam with the deflection angle of the oscillator structure such that thewavelength of the FMCW light beam varies in synchronization with avariance in the deflection angle of the oscillator structure.
 9. Theoscillator system of claim 7, wherein the controller is configured tosynchronize the wavelength of the FMCW light beam with the deflectionangle of the oscillator structure such that each wavelength of the FMCWlight beam is mapped to a different deflection angle of a plurality ofdeflection angles as the deflection angle varies over time.
 10. Theoscillator system of claim 7, wherein the controller is configured tosynchronize the wavelength of the FMCW light beam with the deflectionangle of the oscillator structure such that the length of the forwardramps and the backward ramps is synchronized with an angular range ofthe deflection angle of the oscillator structure.
 11. The oscillatorsystem of claim 10, wherein the controller is configured to control thelength of the forward ramps and the backward ramps in order tosynchronize the length with the angular range of the deflection angle ofthe oscillator structure.
 12. The oscillator system of claim 10,wherein: the minimum wavelength of the FMCW light beam is synchronizedwith a zero deflection angle of the oscillator structure and the maximumwavelength of the FMCW light beam is synchronized with a maximumdeflection angle of the oscillator structure, or the minimum wavelengthof the FMCW light beam is synchronized with the maximum deflection angleof the oscillator structure and the maximum wavelength of the FMCW lightbeam is synchronized with the zero deflection angle of the oscillatorstructure.
 13. The oscillator system of claim 1, wherein the controlleris configured to synchronize a continuous variance of the wavelength ofthe FMCW light beam with a continuous variance of the deflection angleof the oscillator structure.
 14. The oscillator system of claim 1,further comprising: a measurement circuit configured to measure thedeflection angle of the oscillator structure as the deflection anglevaries over time and generate position information based on the measureddeflection angle, wherein the controller is configured to synchronizethe wavelength of the FMCW light beam with the deflection angle of theoscillator structure based on the position information.
 15. Theoscillator system of claim 1, wherein the plurality of wavelength rampscorrespond to an oscillation period of the oscillator structure, theplurality of wavelength ramps including a series of consecutive forwardramps generated over a first half-period of the oscillation period and aseries of consecutive backward ramps generated over a second half-periodof the oscillation period.
 16. The oscillator system of claim 15,wherein the series of consecutive forward ramps includes N forward rampsand the series of consecutive backward ramps includes N backward ramps,wherein N is an integer greater than zero.
 17. The oscillator system ofclaim 15, wherein the transmitter is configured to change a rampingdirection of the plurality of wavelength ramps at a maximum deflectionangle of the oscillator structure.
 18. The oscillator system of claim15, wherein each wavelength ramp of the plurality of wavelength rampscorresponds to one angular sub-range of a plurality of angularsub-ranges that make up a full angular range of the deflection angle ofthe oscillator structure.
 19. The oscillator system of claim 18,wherein: each wavelength ramp of the series of consecutive forward rampscorresponds to a different angular sub-range of the full angular rangeof the deflection angle, and each wavelength ramp of the series ofconsecutive backward ramps corresponds to a different angular sub-rangeof the full angular range of the deflection angle.
 20. The oscillatorsystem of claim 18, wherein: each of the plurality of wavelength rampshave a length corresponding to a time duration each of the plurality oframps takes to transition between a minimum wavelength and a maximumwavelength, and the oscillator system further comprises: a controllerconfigured to control the length of each of the plurality of wavelengthramps in order to synchronize the length with an angular sub-range ofthe full angular range of the deflection angle.
 21. The oscillatorsystem of claim 18, further comprising: a controller configured tosynchronize each of the plurality of wavelength ramps to a correspondingangular sub-range of the plurality of angular sub-ranges.
 22. Theoscillator system of claim 21, wherein the controller is configured tosynchronize the wavelength of the FMCW light beam with the deflectionangle of the oscillator structure such that the wavelength of eachwavelength ramp varies in synchronization with a variance in thedeflection angle over the corresponding angular sub-range.
 23. Theoscillator system of claim 15, wherein: each wavelength ramp of theplurality of wavelength ramps corresponds to one dedicated beampropagation direction of a plurality of dedicated beam propagationdirections, and the dispersive element is configured to compensate theFMCW light beam such that each wavelength of a same wavelength ramp isaligned in a same dedicated beam propagation direction at the output ofthe transmission path.
 24. The oscillator system of claim 23, wherein:each wavelength ramp of the series of consecutive forward rampscorresponds to a different dedicated beam propagation direction of theplurality of dedicated beam propagation directions, and each wavelengthramp of the series of consecutive backward ramps corresponds to adifferent dedicated beam propagation direction of the plurality ofdedicated beam propagation directions.
 25. A method of controlling anoscillator structure, the method comprising: transmitting a frequencymodulated continuous wave (FMCW) light beam along a transmission path,wherein the FMCW light beam comprises a plurality of wavelength rampsand a wavelength of the FMCW light beam continuously varies over time;driving an oscillator structure about a scanning axis based on adeflection angle of the oscillator structure that continuously variesover time, wherein the oscillator structure is arranged in thetransmission path and is configured to direct the FMCW light beam or acompensated FMCW light beam that is derived from the FMCW light beamtowards an output of the transmission path; synchronizing the wavelengthof the FMCW light beam with the deflection angle of the oscillatorstructure; and compensating for a propagation direction disturbancecaused by an oscillation of the oscillator structure to generate thecompensated FMCW light beam such that each wavelength of a correspondingwavelength ramp of the compensated FMCW light beam is aligned in a samedirection at the output of the transmission path.
 26. A method ofcontrolling an oscillator structure, the method comprising: transmittinga frequency modulated continuous wave (FMCW) light beam along atransmission path, wherein the FMCW light beam comprises a plurality ofwavelength ramps and a wavelength of the FMCW light beam continuouslyvaries over time; driving an oscillator structure about a scanning axisbased on a deflection angle of the oscillator structure thatcontinuously varies over time, wherein the oscillator structure isarranged in the transmission path and is configured to direct the FMCWlight beam or a compensated FMCW light beam that is derived from theFMCW light beam towards an output of the transmission path;synchronizing the wavelength of the FMCW light beam with the deflectionangle of the oscillator structure; measuring the deflection angle of theoscillator structure as the deflection angle varies over time; andgenerating position information based on the measured deflection angle;wherein synchronizing the wavelength of the FMCW light beam with thedeflection angle of the oscillator structure is performed based on theposition information.